Apparatus and method for measuring the vertex power of an optical system

What is claimed: 
     
       1. An apparatus for measuring a vertex power of a lens system having a central axis, an effective principal plane, a vertex and a focal point, comprising in combination: means for providing a beam of parallel light rays, said beam being parallel to said central axis at a first predetermined radial distance therefrom, said beam of light impinging on said lens system, said light beam being refracted by said lens system such that said light beam virtually defines a first locus on said principal plane, and effectively passes thererfrom in a straight line through said focal point to tend to define a second locus on an intermediate plane parallel to said principal plane at a first predetermined axial distance along said central axis from said vertex, and illuminating a portion of a subsequent plane parallel to said principal plane positioned a second predetermined axial distance along said central axis from said intermediate plane;   means for effecting a rotational motion between said light beam and said lens system about a rotational axis at a predetermined angular frequency;   means for admitting to said subsequent plane only such portion of said light beam as passes through a third locus within said second locus on said intermediate plane, said third locus being annular and of lesser radial dimension than said second locus, and disposed at a second predetermined radial distance from said central axis, the portions of said light beam as refracted admitted to said subsequent plane defining a fourth locus on said subsequent plane and the portions of said light beam when unrefracted tending to be admitted to said subsequent plane, tending to define a fifth locus on said subsequent plane; and   means responsive to said light beam portions passing through said third locus for providing an indication of the difference in radial position in said subsequent plane of said fourth locus from said fifth locus, whereby said indication is representative of the vertex power of said optical system.   
     
     
       2. The apparatus of claim 1 wherein said indication means comprises a position-sensitive photodetector disposed in said subsequent plane, said photodetector generating an output signal indicative of said radial position difference. 
     
     
       3. The apparatus of claim 2 wherein said output signal is representative of:   r.sub.a d.sub.a (F.sub.B /1-d.sub.v F.sub.B)     where F B  is the vertex power of said optical system, r a  is said predetermined radial distance between said fourth locus and central axis, d v  is said predetermined axial distance between said vertex plane and said intermediate plane, and d a  is said predetermined distance between said intermediate plane and said subsequent plane.   
     
     
       4. The apparatus of claim 1 wherein said indication means comprises means for providing visual indication of said radial position difference. 
     
     
       5. In an apparatus for measuring the vertex power of an optical system having a vertex and a focal point, said apparatus being of the type including means for providing a beam of parallel light rays, said beam being at a predetermined radial distance from and parallel to a predetermined central axis to impinge upon said optical system and is scanned about said central axis, said optical system refracting said light beam such that said light beam effectively passes through said focal point, and tends to define a locus on an intermediate plane and to illuminate a portion of a subsequent plane, said intermediate and subsequent planes being at respective predetermined axial distances from said vertex, and means for providing an indication of radial positional deviations of said light beam in said subsequent plane due to refraction by said optical system, and indication being representative of said refractive properties, the improvement wherein said apparatus further comprises: means for defining an aperture within said locus in said intermediate plane, said aperture being of lesser radial dimension than said second locus and of predetermined radial distance from said central axis, and for admitting to said subsequent plane only such of said refracted light beam as passes through said aperture whereby said radial positional deviation is indicative of the vertex power of said optical system;   said means for defining an aperture comprising a generally opaque mask having a transparent annulus to define said aperture, said mask being disposed in said intermediate plane.   
     
     
       6. The apparatus of claim 5 wherein said indication means provides an output signal representative of:   r.sub.a d.sub.a F.sub.B /(1 - d.sub.v F.sub.B)     where F B  is the vertex power of said optical system, r a  is said predetermined radial distance of said second locus from said central axis, d a  is the axial distance between said intermediate and subsequent planes, and d v  is said axial distance between said vertex and said intermediate plane.   
     
     
       7. In an apparatus for measuring refractive properties of a lens system having a vertex and optical axis, said apparatus being of the type including a light source for providing a collimated light beam, means for positioning said optical system in the path of said light beam such that said light beam is parallel to said optical axis and in a given meridian of said lens system, to produce a refracted light beam, said refracted light beam tending to illuminate a portion of a subsequent plane normal to said optical axis, and means responsive to the radial position of said refracted light beam in said subsequent plane for generating an indicating of said refractive properties in said given meridian, the improvement wherein: said apparatus comprises means for effectively scanning said light beam about an axis parallel to said optical axis and means for rotating said aperture in synchronism with said light beam, said aperture being of pinhole form; and   said refracted light beam describes a locus in an intermediate plane between said lens system and said subsequent plane at a predetermined axial distance from said optical system vertex; and said apparatus further comprises means for admitting to said subsequent plane only such portions of said refracted light beam as pass through a predefined aperture in said intermediate plane, said aperture being within said locus at a predetermined radial distance from said axis and of predetermined radial dimension less than the radial dimension of said locus;   said indication being representative of the difference between the instantaneous radial position in said subsequent plane of said refracted light beam portion and said aperture predetermined radial distance and thereby indicative of the vertex power of said lens system in said given meridian.   
     
     
       8. Apparatus for measuring refractive properties of a sphero-cylindrical optical system having a vertex comprising: means for producing a collimated light beam of predetermined radial beam width;   means for effecting a circular scanning of said light beam parallel to a predetermined rotational axis at a predetermined scanning radius to illuminate said optical system and produce a scanned refracted beam;   a generally opaque mask disposed at a predetermined axial position from said vertex, said mask including a transparent annulus portion of predetermined radius and radial width, said transparent annulus being disposed in the path of said refracted light beam, said annulus radial width being less than said predetermined radial beam width;   photodetector means positioned at a predetermined axial distance from said mask for generating an output signal indicative of change in radial distance of the instantaneous point of intersection of said light beam with said photodetector due to refraction by said optical system from said predetermined radius; and   signal processing means responsive to said photodetector output signals for generating signals indicative of said refractive properties.   
     
     
       9. The apparatus of claim 8 wherein said annulus radius is substantially equal to said scanning radius. 
     
     
       10. In an apparatus for measuring refractive properties of a lens system having a vertex and optical axis, said apparatus being of the type including a light source for providing a collimated light beam, means for positioning said optical system in the path of said light beam such that said light beam is parallel to said optical axis and in a given meridian of said lens system to produce a refracted light beam, the apparatus comprising means for effectively scanning said light beam about an axis parallel to said optical axis, said refracted light beam tending to illuminate a portion of a subsequent plane normal to said optical axis, and means responsive to the radial position of said rafracted light beam in said subsequent plane for generating an indication of said refractive properties in said given meridian, the improvement wherein: said refracted light beam describes a locus in an intermediate plane between said lens system and said subsequent plane at a predetermined axial distance from said optical system vertex, and said apparatus further comprises means for admitting to said subsequent plane only such portions of said refracted light beam as pass through a predefined aperture in said intermediate plane, said aperture being within said locus at a predetermined radial distance from said axis and of predetermined radial dimension less than the radial dimension of said locus;   said aperture being in the form of a circular annulus of constant radius and radial width and centered on said rotational axis; and   said indication being representative of the difference between the instantaneous radial position in said subsequent plane of said refracted light beam portion and said aperture predetermined radial distance and thereby indicative of the vertex power of said lens system in said given meridian.   
     
     
       11. The apparatus of claim 10 wherein said indication means provides an output signal substantially equal to:   r.sub.a d.sub.a F.sub.B /(1 - d.sub.v F.sub.B)     where F B  is the vertex power of said optical system, r a  is said fourth locus predetermined radial distance, d a  is the distance between said intermediate and subsequent planes and d v  is said predetermined distance between said intermediate plane and said optical system vertex.